The invention relates to a method for determining the drawbar length of a trailer of a tractor vehicle according to preamble the claim 1 and the use of this method to determine a maximum permissible articulation angle between the tractor vehicle and its trailer.
Maneuvering a vehicle combination, as for example a passenger car or a truck with trailer, in particular a single-axle trailer according to the German Highway Code, requires a high skill level from a driver of such vehicle. The articulation angle between the longitudinal axis the tractor vehicle and a trailer drawbar attached by a drawbar represents an additional degree of freedom which may cause instabilities during reverse travel which must be compensated by the driver via appropriate steering angle corrections. When a maximum articulation angle is exceeded, there is a risk that the trailer jackknifes unless the brake is applied early enough or forward travel is commenced. An articulation angle beyond the maximum articulation angle can be reduced only by driving forward in a straight line.
The kinematic and dynamic behavior of a trailer during maneuvering, in particular jackknifing during reverse maneuvers, depends on the distance between the ball head of the trailer coupling and the hitch the drawbar, respectively, and the axle of the trailer. An effective drawbar length can be defined for multi-axle trailers, for example, the distance of a point between the hitch and a point located between the two axles of the trailer.
For example, the maximum allowable articulation angle, at which the trailer can still be straightening in reverse is about 25° for a short trailer with a drawbar length from 1.5 m, whereas for a long trailer with a drawbar length from 4.9 m this value increases to about 85°. These exemplary values apply to a wheelbase of about 3 m and a distance from ball head to the rear-axle of the trailer of about 1 m when only the front-axle of the tractor vehicle is steered.
It would therefore be possible to have a maneuvering assistant of the tractor vehicle use the full maneuvering space of the tractor-trailer combination by determining the maximum permissible articulation angle for vehicles with and without rear-axle steering. If such drawbar length not known, the maneuvering assistant would start with a maximum permissible articulation angle obtained from the shortest possible drawbar length of a permitted trailer.
In order to fully use the maneuvering space of a tractor-trailer combination for the actually attached trailer, its drawbar length must be known.